Hopper-shaped truck bodies having bottom conveyors are used for slowly conveying material out through a metering opening to a spreader, usually in the form of a spinner device. U.S. Pat. No. 3,790,090 suggests a way of operating such a body to dump a whole load quickly by providing, in addition to a metering door, a pivoted rear dump gate such as used on tilting dump bodies. Then by moving the spinner mechanism aside and running the conveyor at high speed, it is possible to unload rapidly through the open rear gate.
The invention involves recognition of a better way of achieving spreading and both full and partial dumping from a hopper-shaped truck body having a bottom conveyor. The invention simplifies the necessary structure, eliminates manual operation, provides for full power control, and allows simple and convenient changing between spreading at slow rates and dumping at a maximum rate. It also suggests an improved and simplified way of making a spinner device quickly detachable from a truck body for dumping and easily reattachable to the body for spreading.